Norepinephrine

Norepinephrine (INN) (abbreviated norepi or NE) is the US name for noradrenaline (BAN) (abbreviated NA or NAd), a catecholamine with multiple roles including as a hormone and a neurotransmitter. Areas of the body that produce or are affected by norepinephrine are described as noradrenergic.

The terms noradrenaline (from the Latin) and norepinephrine (derived from Greek) are interchangeable, with noradrenaline the common name in most parts of the world. However, to avoid confusion and achieve consistency medical authorities have promoted norepinephrine as the favoured nomenclature, and this is the term used throughout this article.

One of the most important functions of norepinephrine is its role as the neurotransmitter released from the sympathetic neurons affecting the heart. An increase in norepinephrine from the sympathetic nervous system increases the rate of contractions.

As a stress hormone, norepinephrine affects parts of the brain, such as the amygdala, where attention and responses are controlled. Along with epinephrine, norepinephrine also underlies the fight-or-flight response, directly increasing heart rate, triggering the release of glucose from energy stores, and increasing blood flow to skeletal muscle. It increases the brain's oxygen supply. Norepinephrine can also suppress neuroinflammation when released diffusely in the brain from the locus coeruleus.

When norepinephrine acts as a drug it increases blood pressure by increasing vascular tone (tension of muscles) through α-adrenergic receptor activation. The resulting increase in vascular resistance triggers a compensatory reflex that overcomes the direct homeostatic effect of that increase on the heart, called the baroreceptor reflex, which otherwise would result in a drop in heart rate called reflex bradycardia.

Norepinephrine is synthesized from dopamine by dopamine β-hydroxylase. It is released from the adrenal medulla into the blood as a hormone, and is also a neurotransmitter in the central nervous system and sympathetic nervous system where it is released from noradrenergic neurons in the locus coeruleus. The actions of norepinephrine are carried out via the binding to adrenergic receptors.